Converting Between Speed Units: MPH, KPH & Knots

Speed units vary depending on where you are and what you’re doing. Drivers in the United States watch for speed limits in miles per hour, while drivers in Germany read their speedometers in kilometers per hour. Pilots and sailors worldwide measure speed in knots. Knowing how to convert between these units is practical for international travel, understanding weather reports, or simply making sense of a speed reference from another country.

This guide covers the three most common speed units, explains the conversion formulas, and describes the real-world contexts where each one applies.

The Three Main Speed Units

Miles Per Hour (mph)

Miles per hour is the standard speed unit in the United States, the United Kingdom (for road signs), and a few other countries including Myanmar and Liberia. One mile equals 5,280 feet or approximately 1.609 kilometers.

Common reference points in mph:

Walking speed: 3 mph
City driving: 25-35 mph
Highway driving: 55-75 mph
Professional baseball pitch: 90-100 mph
Speed of sound at sea level: approximately 767 mph

Kilometers Per Hour (km/h or kph)

Kilometers per hour is used by the vast majority of the world’s countries for road speed limits, automotive speedometers, and general-purpose speed measurements. One kilometer equals 1,000 meters or approximately 0.621 miles.

Common reference points in km/h:

Walking speed: 5 km/h
City driving: 40-60 km/h
Highway driving: 90-130 km/h
High-speed train (TGV): 320 km/h
Speed of sound at sea level: approximately 1,235 km/h

Knots (kn or kt)

A knot equals one nautical mile per hour. One nautical mile is exactly 1,852 meters, which is the length of one minute of arc of latitude on the Earth’s surface. This geographic basis is why knots are the standard in aviation and maritime navigation.

Common reference points in knots:

Gentle sailing breeze: 10-15 knots
Cruise ship speed: 20-24 knots
Commercial aircraft cruising speed: 450-530 knots
Tropical storm threshold: 34 knots
Hurricane threshold: 64 knots

Conversion Formulas

The exact conversion factors between these units are:

From	To	Multiply by
mph	km/h	1.60934
km/h	mph	0.621371
mph	knots	0.868976
knots	mph	1.15078
km/h	knots	0.539957
knots	km/h	1.852

MPH to KPH

Multiply the mph value by 1.60934.

Example: 65 mph x 1.60934 = 104.6 km/h

Quick estimation: Multiply by 1.6. For 65 mph: 65 x 1.6 = 104 km/h. Close enough for practical purposes.

An even quicker mental trick uses the Fibonacci sequence. Consecutive Fibonacci numbers (1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89…) have a ratio that approaches 1.618, which is very close to the mph-to-kph conversion factor of 1.609. So 55 mph is roughly 89 km/h, 34 mph is roughly 55 km/h, and 89 mph is roughly 144 km/h.

KPH to MPH

Multiply the km/h value by 0.621371.

Example: 120 km/h x 0.621371 = 74.6 mph

Quick estimation: Multiply by 0.6. For 120 km/h: 120 x 0.6 = 72 mph.

MPH to Knots

Multiply the mph value by 0.868976.

Example: 100 mph x 0.868976 = 86.9 knots

Quick estimation: Subtract about 13% from the mph value. For 100 mph: 100 - 13 = 87 knots.

Knots to MPH

Multiply the knot value by 1.15078.

Example: 500 knots x 1.15078 = 575.4 mph

Quick estimation: Add about 15% to the knot value.

KPH to Knots

Multiply the km/h value by 0.539957.

Example: 250 km/h x 0.539957 = 135 knots

Quick estimation: Divide by roughly 1.85.

Knots to KPH

Multiply the knot value by 1.852.

Example: 30 knots x 1.852 = 55.6 km/h

This is an exact conversion since one nautical mile is defined as exactly 1,852 meters.

Why Different Units Exist

Historical Origins of MPH

The mile has its roots in the Roman “mille passus” (a thousand paces), and English-speaking countries adopted it as their standard distance unit centuries ago. When vehicles appeared, speed was naturally expressed in miles per hour. The United States, having built its entire road infrastructure around miles, hasn’t switched.

The Metric System and KPH

The metric system was developed during the French Revolution to create a universal, decimal-based measurement standard. The kilometer, defined as one-thousandth of the distance from the equator to the North Pole (approximately), became the standard distance unit for most of the world. Speed in km/h followed naturally.

Why Aviation and Maritime Use Knots

The nautical mile is based on the geometry of the Earth. Because one nautical mile equals one minute of latitude, navigation calculations on charts are simpler. If you need to travel 60 nautical miles due north, you know that is exactly one degree of latitude. This direct relationship between distance and the coordinate system makes knots indispensable for air and sea navigation, even in countries that otherwise use the metric system.

Real-World Conversion Scenarios

International Road Trips

When driving from the United States into Canada or from the UK to continental Europe, speed limit signs change units at the border. A 100 km/h sign in Canada is about 62 mph. A 130 km/h motorway in France is about 81 mph. Knowing the rough conversion prevents tickets and confusion.

Weather Reports

Wind speed is reported differently depending on the source:

US weather reports typically use mph.
Most international weather services use km/h.
Maritime forecasts and tropical storm advisories use knots worldwide.
The Beaufort Scale, used in shipping forecasts, is defined in knots.

When a hurricane advisory says “sustained winds of 120 knots,” that is 138 mph or 222 km/h. When your weather app says winds of 40 km/h, that is 25 mph or 22 knots.

Sports

Baseball: Pitch speed is measured in mph in the US and km/h in Japan and South Korea. A 100 mph fastball is a 161 km/h fastball.
Tennis: Serve speeds at international tournaments are shown in km/h. A 230 km/h serve is a 143 mph serve.
Cycling: European races report speeds in km/h. A peloton averaging 45 km/h is moving at 28 mph.
Motorsport: Formula 1 uses km/h; NASCAR uses mph. Top F1 speeds around 370 km/h translate to about 230 mph.

Aviation

Even American pilots use knots for airspeed. When air traffic control says “reduce speed to 250 knots,” that is non-negotiable and universal. Runway visibility and wind conditions are also reported in knots. If you read a flight tracker showing your plane at 480 knots, that is 553 mph or 889 km/h.

Other Speed Units

While mph, km/h, and knots cover the vast majority of everyday speed references, a few other units appear in specialized contexts:

Meters per second (m/s): Used in physics and by some weather services. Multiply m/s by 3.6 to get km/h or by 2.237 to get mph.
Feet per second (ft/s): Sometimes used in ballistics and engineering. Multiply ft/s by 0.6818 to get mph.
Mach number: The ratio of speed to the speed of sound. Mach 1 is approximately 767 mph, 1,235 km/h, or 667 knots at sea level. The exact value varies with temperature and altitude.

Use the Tool

For instant and precise conversions, our Speed Converter handles all common speed units. Enter a value in any unit and see the equivalent in every other unit simultaneously. It’s especially useful when comparing speeds from different sources, such as checking whether a storm’s 80-knot winds translate to hurricane force on the mph scale.

Frequently Asked Questions

Why does the UK use mph for driving but km for running events?

This is a legacy of partial metrication. The UK officially adopted the metric system for most purposes but kept imperial units for road signs and speed limits. Athletics, governed by international bodies, uses kilometers. So a British runner trains in kilometers and drives home watching for mph signs. There have been proposals to switch road signs to metric, but the cost and public resistance haven’t led to any change.

How fast is Mach 1 in miles per hour?

At sea level and at 59 degrees Fahrenheit (15 degrees Celsius), Mach 1 is approximately 767 mph (1,235 km/h or 667 knots). However, the speed of sound varies with temperature and altitude. At cruising altitude (35,000 feet), where the air is much colder, Mach 1 drops to roughly 660 mph. This is why supersonic speeds are expressed as Mach numbers rather than fixed mph values.

Is a knot the same as a nautical mile?

No. A knot is a unit of speed, equal to one nautical mile per hour. A nautical mile is a unit of distance, equal to 1,852 meters or about 1.151 statute miles. Saying “knots per hour” is incorrect because it would mean nautical miles per hour per hour, which is a unit of acceleration, not speed.

Why do car speedometers show both mph and km/h?

Manufacturers sell cars in multiple markets, so dual-unit speedometers save production costs. A car sold in the US, Canada, and the UK needs mph. The same model sold in continental Europe needs km/h. Printing both scales on one dial or digital display means one speedometer works everywhere. It also helps drivers who cross borders between countries using different units.

What is the fastest speed ever recorded for a land vehicle?

The current land speed record is 763.035 mph (1,227.985 km/h or 662.75 knots), set by ThrustSSC in the Black Rock Desert, Nevada, in 1997. This speed exceeds Mach 1 at ground level, making ThrustSSC the first car to officially break the sound barrier. The record has stood for nearly three decades.